Add specs for IO.open to close the file descriptor if block raises

It did have some checks if the close operation raises, but not what
happens if the block itself raises an exception.

core/io/open_spec.rb

@@ -37,6 +37,19 @@
     ScratchPad.recorded.should == :called
   end
 
+  it "propagate an exception in the block after calling #close" do
+    -> do
+      IO.open(@fd, "w") do |io|
+        IOSpecs.io_mock(io, :close) do
+          super()
+          ScratchPad.record :called
+        end
+        raise Exception
+      end
+    end.should raise_error(Exception)
+    ScratchPad.recorded.should == :called
+  end
+
   it "propagates an exception raised by #close that is not a StandardError" do
     -> do
       IO.open(@fd, "w") do |io|